The invention relates to a photomultiplier tube and particularly to an improved structure for electrically contacting a photocathode of a photomultiplier tube.
U.S. Pat. No. 2,829,293 issued to Widmaier on Apr. 1, 1958, shows a conventional point cathode contact member comprising a resilient wire which is biased to bear against a small area of a metal film which is evaporated onto the interior surface of a tube envelope adjacent to a faceplate. A photocathode which is formed on the faceplate slightly overlaps a portion of the metal film. A metal lead is connected between the resilient wire and the cathode lead which extends beyond the tube. Generally, the metal film is aluminum of nickel or some other easily evaporated metal which adheres well to glass. Conventional cathode contact members are either the point contact type described in the Widmaier patent or a tab-type contact member such as that shown in U.S. Pat. No. 2,160,593 issued to Kling on May 30, 1939 and in U.S. Pat. No. 3,372,967 issued to Hughes on Mar. 12, 1968. As shown in the Kling patent, the tab contact member bears upon a slightly larger area than the point contact member of Widmaier; however, each type of contact member relies on a biasing spring which is supported or affixed at one end to provide a cantilever electrical connection to the cathode. It is well known in the art that both point and tab-type cantilever contact members are electrically and mechanically unreliable and tend to physically abrade the metal film at the area of contact and eventually cause tube failure due to electrical arc-over or burn-through of the abraded metal film adjacent to the contact member.